<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>过渡</title>
    <style>
        .root{
            width: 100px;
            height: 100px;
            background-color: green;
            transition: all 2s ;  /* 省略 ease 0s */
        }

        .root:hover{
            width: 400px;
            height: 400px;
            background-color:yellow;
        }
    </style>
</head>
<body>
    <div class="root">

    </div>

</body>
</html>